Electric overload switch with improved thermal actuator



Dec. 28, 1965 R. w. THOMAS ETAL 3, 6,5 0

ELECTRIC OVERLOAD SWITCH WITH IMPROVED THERMAL ACTUATOR Filed Sept. 20,1962 6 Sheets-Sheet 1 INVENTORS /Z0557' M 7204445 4 n/ao 0 7.- Pa: 7-2

Dec. 1965 R. w. THOMAS ETAL 3,

ELECTRIC OVERLOAD SWITCH WITH IMPROVED THERMAL ACTUATOR Filed Sept. 20,1962 x 6 Sheets-Sheet 2 INVENTORS 05527 [1/ THOMAS [4 W000 2' PlA 7-21965 R. w. THOMAS ETAL 3,226,510

ELECTRIC OVERLOAD SWITCH WITH IMPROVED THERMAL ACTUATOR Filed Sept. 20,1962 6 Sheets-Sheet 5 & w R

n U ll "2 w. INVENTORS \Q 206597 1147404445 ilk/000 z P4472 Dec. 28,1965 R. w. THOMAS ETAL ELECTRIC OVERLOAD SWITCH WITH IMPROVED THERMALACTUATOR Filed Sept. 20, 1962 6 Sheets-Sheet 4 A M A -ml bw INVENTORS0aer M Tye/v45 504 000 7? PATZ 0376045445 f iaag/eag Ja /EN 4rraeA//s R.w. THOMAS ETAL 3,226,510

ELECTRIC OVERLOAD SWITCH WITH IMPROVED THERMAL ACTUATOR Dec. 28, 1965 6Sheets-Sheet 5 Filed Sept. 20, 1962 MQ NQ \Q G U .N

ATTOEA/EYS R. W. THOMAS ETAL Dec. 28, 1965 ELECTRIC OVERLOAD SWITCH WITHIMPROVED THERMAL ACTUATOR 6 Sheets-Sheet 6 Filed Sept. 20, 1962INVENTORS eaaaer M THOMAS Aim/000 7. PzAT'Z ATTOIQ/VE K5 United StatesPatent Ofilice ELECTRIC OVERLOAD SWITCH WITH IM- PROVED THERMAL ACTUATORRobert W. Thomas, St. Clair Shores, and Elwood T.

Platz, Grosse Pointe Farms, Mich, assignors to I-T-E Circuit BreakerCompany, Philadelphia, Pa., :1 corporation of Pennsylvania Filed Sept.20, 1962, Ser. No. 225,044

12 Claims. (Cl. 200-122) Our present invention relates to an overloadrelay and more particularly to a novel arrangement whereby each pole ofa multi-pole arrangement is provided with a separate and distinctplug-in device, with all of the devices connected in electrical seriesfor electrical coordination. Our novel overload relay device isconstructed to be used as an independent piece of apparatus or inconjunction with a contactor to form a motor starter.

Essentially, our invention consists of a plug-in device a unitaryassembly comprised of (a) a heating circuit, (b) a control circuit, (c)and adjustment means, (d) lost motion connector, (e) external control,and an adapter plate to which a plurality of the plug-in devices aremounted.

A. HEATER CIRCUIT The heater circuit is constructed so that the heaterterminals are readily accessible from the external portion of the casingand the heater, therefore, is readily removable and replaceable withoutdisassembling the casing.

Our device is so constructed so that a variety of heaters can be used,as for example, a U-shaped heater, a coilwound heater, or a two-pieceheater, depending on the electrical requirements of the circuit. Whenthe overload relay is used with a contactor, the arrangement is suchthat one terminal of the heater is electrically connected to the maincontacts of the contactor and the other terminal provides a connectionpreferably to the load terminal.

B. CONTROL CIRCUIT Within the same casing containing the heater circuit,a control circuit is located which comprises not only the controlcontacts for the control coil of the contactor, but also the auxiliaryor signal contacts.

Essentially, the control circuit is comprised of a pivoted contact armwhich forms one leg of a toggle and a biasing spring which forms theother leg of the toggle. The contact arm is constructed in such a mannerthat it is pivoted at a central point and carries the main contacts atone end and the auxiliary or signal contacts at the other end thereof.The control circuit is further constructed so that the terminals whichprovide the energization for the main contacts can either be plug-interminals or standard screw type terminals. With the plug-inarrangement, the overload relay can be easily mechanically andelectrically connected to a contactor by the simple expedient ofproviding an adapter plate with the contactor.

C. ADJUSTMENT DEVICE The overload sensing means of our overload relay iscomprised of a bimetal which is mounted on a support means comprised ofa main support and auxiliary support. The auxiliary support is securedin position by a field adjustment means although the main and auxiliarysupport can be moved relative to each other means of a separate anddistinct factory calibration means. Both the factory calibration meansand the field adjustment means are provided to permit a change in theposition of the bimetal relative to the heater without distorting the bimetal.

3,226,510 Patented Dec. 28, 1965 The auxiliary support is constructed asa Z-shaped member with the connecting end and particularly the bend ateach end being purposely made weak to permit factory calibration. Thebimetal is secured at a first end and the other end thereof is free todeflect upon heating of the bimetal. There is an internal surface of thecase which serves as a pivot for the assembly of the bimetal, the mainsupport and, the auxiliary support.

D. LOST MOTION CONNECTOR As previously noted, the control circuitcomprises a bimetal whose free end can be adjustably positioned and thecontrol circuit comprises a toggle mechanism, one leg of which is abiasing spring. A lost motion translator is provided whereby movement ofthe bimetal away from the heater upon the occurrence of an overloadcurrent is transmitted through the translator to reposition the togglespring so that the toggle is driven over-center thereby resulting in thesimultaneous opening of the main contacts and closing of the auxiliaryor signal contacts. However, as the bimetal cools the toggle spring isnot moved back over center by the translator because of a lost motionarrangement.

E. EXTERNAL CONTROL Means are provided in our novel overload relaywhereby a single unit can perform several functions, such as a manualopening operation, a pre-set for automatic re-set operation, a manualre-set of the contacts from the open to the closed position, as well asmanual opening plus lock-off. In essence, there is a plunger deviceprovided with a first and second cam surface. The plunger device can beselectively altered so that with the first cam surface on the plungerthe device can be manually opened even though the second cam surface ison the plunger. On the other hand, if it is desired to have automaticre-set operation, the first cam surface can be removed from the plungerand the second cam surface will thereby function as an automatic re-setmeans. When the plunger is utilized as a manual opening device, afirstlock-off means can be provided to hold the plunger in the fixedposition and when the plunger is used as an automatic re-set device thesame locking means can be used to hold the plunger in position.

Thus, the plunger is provided with a first and second cam surface withthe first cam surface utilized exclusively for manual opening operationand when the plunger has both a first and second cam surface, the secondcam surface functions as a manual re-set surface. However, when thefirst cam surface is removed, the second cam surface functions both as amanual re-set surface and an automatic re-set surface. It should benoted that the plunger means is removable without disassembling thehousing so that the first cam surface can readily be removed in thefield, if so desired, without affecting the factory calibration orassembly.

It should be noted that the second cam surface, although in physicalcontact with the contact arm, merely moves the contact arm over centerand does not physically drive the contact arm completely to the engagedposition. That is, the second cam surface merely repositions the toggleand this permits the spring of the toggle to serve as the quick-closemeans for the contact. Hence, the plunger in all positions thereof willpermit a trip-free operation. It should be noted that undesirablepumping operation will not result since there is not an instantaneoustrip means. That is, the main contacts will close and will not be movedto the open posi- :tion until the bimetal is heated again but when thebimetal is heated, the contacts will be free to move in the openposition until they engage the second cam surface.

F. ADAPTER PLATE Means are provided whereby the base of the contactorcan be extended to provide a mechanical support as well as theelectrical connection for a plurality overload relay units. Inparticular, the adapter plate is provided with plug-in contacts andconnecting straps that will automatically connect all of the maincontacts of the overload relays in electrical series.

The adapter plate if further provided with keying means or a recess toreceive protrusions from the overload relay so that the overload relayplug-in contacts are in alignment with the female contacts of theadapter plate and also to insure that the heater terminal is inalignment with a terminal of the contactor.

Accordingly, a primary object of this invention is to provide a novelconstruction for an overload relay device.

Another object is to provide a novel overload relay of relatively simpleconstruction which possesses reliable operating characteristics.

Still another object is to provide an overload relay having novel meansfor mounting of the bimetal.

A further object is to provide an overload relay having novel means fortripping and lockout.

A still further object is to provide an overload relay having a novelarrangement of the bimetal, motion translator, and toggle switchmechanism.

These and other objects of our invention will be obvious from thefollowing description taken in connection with the drawings, in which:

FIGURE 1 is an exploded perspective showing the heater circuit, controlcircuit and adjustment means of our novel overload relay.

FIGURE 2 is a side view of the overload relay with the cover removed.

FIGURE 4 is a view of the other side of the casing of the overloadrelay.

FIGURE 5 is a top view of the overload relay of FIGURE 2.

FIGURE 2a i a composite side and cross-sectional view similar to FIGURE2 but illustrates the movement of the bimetal, the heater circuit, andthe configuration of the plunger.

FIGURES 3a 3c are various end cross-sectional views of the motor starterin which FIGURE 3a is taken along line 3a-3a of FIGURE 2a looking in thedirection of the arrows 3a-3a; FIGURE 3b is taken along the line 3b3b ofFIGURE 2a looking in the direction of arrows 3b-3b; and FIGURE 3c is anend view of the device of FIGURE 2 taken from the right end.

FIGURE 6a is an illustration of a two-piece heater that may besubstituted for the U-shap-ed heater of FIG- URES l and 2.

FIGURE 6b is an illustration of a coil type heater.

FIGURE 6c is a side elevation of a slide utilized for manual tripping ofthe overload relay.

FIGURE 7a is a top view of the adapter plate.

FIGURE 7b is an end view of the adapter plate of FIGURE 7a.

FIGURE 7c is a side view taken in the direction of the arrows 7c7c ofFIGURE 7a.

FIGURE 7d is a perspective showing the construction of the femaleplug-in contacts.

FIGURE 8 is a composite plan view illustrating the overload relay andadapter plate of our invention in conjunction with a contactor.

Now referring to the figures and more particularly to FIGURES 1 through5. Overload relay unit 10 consists of a molded housing divided alongline 11 to form base 12 and cover 13 joined by screws 75. In a mannerwell-known to the art, base 12 and cover 13 are provided with internaldepressions and protrusions which engage the electrical and activemechanical elements of unit 10 to operatively position these elements.

With respect to FIGURE 2a, there is a top opening 14 which forms anentrance to main cavity 15 in base 12. Disposed externally of housing 10at the top thereof are spaced apart main circuit terminals 16, 17, (asshown in FIG. 1) each of which are generally L-shaped. A generallyU-shaped resistance heater element 18 is disposed within main cavity 15and is provided with outturned legs 18a at the free ends of the U arms.Outturned legs 18a are provided with clearance apertures which receivescrews 1? for securing heater 18 to terminals I6, 17. An auxiliary wireconnector 17a is mounted to extension 17b of terminal 17.

Disposed within cavity 15 and extending generally parallel to one of thelegs of heater I8 is a bi-metallic element 21. The upper end of element21 is fixedly secured as by welding to the upper end of main supportmember 22. Main support 22 extends between the arms 23 at the bifurcatedupper end of auxiliary support 24 and is secured to auxiliary support 24near the free ends of arms 23. The lower end of supports 22 and 24 arejoined together by factory calibration screw 25 extendingthrough slot 26in auxiliary support 24 and is received in a threaded aperture of mainsupport 22. It is noted that arms 23 have two bends therein and that thecross-sectional areas of both arms 23 is less than the cross-sectionalarea of main support 22. Thus, upon manipulation of screw 25 themovement of main support member 22 relative to auxiliary support member24 is accomplished by bending auxiliary support member 24.

At a point intermediate its ends, auxiliary support member 24 isprovided with a threaded aperture which receives field adjustment screw27 whose enlarged head 23 is disposed externally of housing 12, 13.Bowed leaf spring 28 is disposed within main cavity 15 with the endsthereof bearing against base 12 and the center portion thereof bearingagainst auxiliary support member 24 at a point thereof near its lowerend. The action of spring 28 urges main support member 22 to seat itselfagainst bearing surface 29 internal of base 12. Surface 29 forms a fixedpoint of reference about which bimetal 21 moves upon deflection thereof.Bimetal 21 is so constructed that the lower end thereof is free todeflect to the right with respect to FIGURE 2 when bimetal 21 is heated.

Bimetal 21, upon deflection thereof, acts through translator bar 31 toseparate movable contact 32 from stationary contact 33 in a manner to behereinafter explained. Stationary contact 33 is mounted to one end ofconducting strap 34 whose other end constitutes plug-in terminal 35extending from the bottom of housing 12, 13. Movable contact 32 ismounted to the upper end of contact arm 36 provided with bifurcatedsections 37 whose free ends are entered into depressions 38 whichconstitute pivot points for movable contact arm 36. Depres-sions 38 areformed in the upper surfaces of spaced projections 41 extendinghorizontally from conducting strap 39 at a point intermediate the endsthereof. The lower end 40 of strap 39 constitutes a plug-in terminalextending externally of housing 12, 13.

Spring 47 is connected at its lower end to adjust-able screw 48 and isconnected at its upper end to contact arm 36. The center line of spring47 extends to the left of the pivot 3% of movable contact arm 36 as seenin FIG- URE 2 to thereby exert a force on the movable contact 32 to theleft. However, when the bimetal 21 is heated to cause movement of thetranslator bar 31, the center line of spring 47 is moved to the right ofthe pivot 38 to thereby exert a force on the movable contact to theright as best seen in FIGURE 2(a).

Movable contact arm 36 includes a downwardly extending portion 42positioned between arms 37 and extending between projections 41. Spring47 is secured to the inner end of adjusting screw 4-8. Screw 48 isthreadably mounted to conducting strap 39. Base 12 is provided withaperture 49 through which the slotted end of screw 48 is accessible foradjustment. The position of screw 48 positions the lower end of spring47 thereby determining the point at which contacts 32, 33 will part asspring 47 is moved to the right by translator bar 31 upon base 12. Theapex of spring 52 is disposed below the head of screw 55 which securesspring 52 to base 12. Spring 52 is partially loaded in a direction suchthat the arms thereof are urged to separate thereby urging slide 50 toits outward position illustrated in FIGURE 2. In this position inclinedreset surface 57 at the lower end of slide 50 is so positioned that Whentranslator bar 31 moves the spring 47 sufliciently to the right ofnotches 38, with respect to FIGURE 2, movable contact 32 separates fromstationary contact 33 by a sufficient distance so that upon cooling ofbimetal 21 contacts 32, 33 will not automatically close.

With contacts 32, 33 separated, after reset slide 50 is moved downwardwith respect to FIGURE 2, surface 57 engages the upper end of contactarm 36 driving movable contact arm 36 over center to the left so thatspring 47 is effective to move contact 32 into engagement with contact33.

For automatic resetting, slide 513 is moved inward to a position wherenotch 61 is in line with locking member 58. Thereafter member 58 ismoved to the left with respect to FIGURE 2 into notch 61. Looking screw62, extending through elongated slot 58a of member 58, maintains member58 in adjusted position.

Factory calibration for bimetal 21 is achieved by manipulating screw 25.As screw 25 is adjusted main support 22 and bimetal 21 are bodily movedas a unit. During this period. of time auxiliary support 24 isessentially stationary although the upper portion thereof deforms topermit the aforesaid movement of main support 22. Field adjustment knob23 is operated to rotate screw 27. This movement brings about the bodilymovement of auxiliary support 24, main support 22 and bimetal 21 as aunit with bearing surface 29 acting as a pivot. It is noted that knob 28is provided with a radial projection 63 which cooperates with base stop64 to limit rotation of screw 27 to approximately one revolution.

It is noted that device 16 as hereinbefore described does not providefor manual tripping. Such provisions may readily be provided by removingreset slide 50 and replacing same by tripping slide 50a. Slide Stlacontains all of the features of slide 50 and in addition contains aportion 70 at its lower end including tripping cam surface 71. It isnoted that portion 79 is connected to the remainder of slide 50a at aweakened section 72 which defines a fracture line so that portion '70can be broken away should it be desired to eliminate the manual trippingfeature.

Slide 56a may be substituted for slide 50 merely by removing spring tip51 from notch 53 thereby permitting slide 50 to be moved upward out ofhousing 12, 13. Thereafter slide Stla is inserted and is maintained inoperative position by placing spring tip 51 into notch 53a when thelatter becomes viewable at base window 73.

With contacts 32, 33 in closed position, downward movement of slide 50afrom the fully projected position brings tripping cam surface 71 intoengagement with movable contact arm 36 moving the latter clockwise aboutpivot depressions 38 to separate contact 32 from contact 33. Uponsubsequent release of slide 50:: spring 52 moves slide 50a upwardthereby permitting spring 47 to move contact 32 back into engagementwith contact 33.

Should contacts 32, 33 be separated through the deflection of bimetal 21these contacts may be brought back into engagement after cooling ofbimetal 21 by depressing slide 50a. This movement of slide 50a bringscam surface 5711 into engagement with upper end of movable contact arm36 moving the latter counterclockwise to a position where the toggle isover center to the left with respect to FIGURE 2 thereby permittingspring 47 to drive movable contact arm 36 into engagement with trippingcam surface 71 and upon release of slide 50a movable contact 32 willengage stationary contact 33.

In order to maintain contacts 32, 33 disengaged, as during a period whenrelated equipment is being serviced, slide Stla may be maintained in itsinward position by moving locking member 58 to the left, with respect toFIGURE 2, into slot 61a at the edge of manual tripping slide 50a.

In the device hereinbefore described, the bimetal heater consists of asingle piece U-shaped resistance element 18. Element 18 may readily bereplaced without removing screw 75 which secures cover 13 to base 12.That is, it is merely necessary to remove screws 19 from terminals 16,17 and thereafter move heater 18 upward with respect to FIGURE 2.

Heater 18 may be replaced by either of the heater constructionsillustrated in FIGURES 6a or 6b. The heater assembly 1611 of FIGURE 61!comprises copper conducting strap 131 whose out-turned end 152 isadapted to abut terminal 16. Heater assembly 16-9 also includesresistance leg 163 extending generally parallel to leg 161 and spacedtherefrom. The outwardly turned end 164 of leg 103 is adapted to abutterminal 17. Legs 161 and 103 are combined as by welding at 165. Inheater assembly 100, heating is concentrated in leg 103 which ispositioned closer to bimetal 21 than is leg 1111. For some applicationsbimetal 21 appears to be more sensitive to heat generated by heater 103than by heater 18.

FIGURE 6b illustrates a heater in the form of resistance wire which isspiraled about insulating support in two layers. The eyelet connectedends 111, 112 of coil 116 are adapted to be connected to terminals 16and 17 by means of screws 19.

With contacts 32, 33 in engagement a complete electrical path existsbetween plug-in terminals 35 and 40. This path comprises terminal 35,conducting strap 34- to stationary contact 33, movable contact 32,movable contact arm 36, and conducting strap 39 to terminal 40. Thisseries circuit is intended to be connected in series with the operatingcoil for contactor 260 as shown in FIG- URE 8.

With reset slide 56 or tripping slide Stla in the fully extendedposition and contacts 32, 33 disengaged contacts 43, 44 will be inengagement. This completes a series circuit extending from terminal 40through con-ducting strap 39, movable contact arm 36, extention 42,movable contact 43 through stationary contact 44, and strap 4-5 toterminal member 46. The last noted circuit is used for signallingpurposes to indicate when unit 16 has been tripped open and must bemanually reset.

Overload relay units of the type described are usually in conjunctionwith contactors for controlling the energization of motors. Thiscombination is effectively achieved by providing plug-in base asillustrated in FIGURES 7a-7d. When used in conjunction with a threephase contactor 200, plug-in base 150 comprises three pairs of spacedcontact receiving jaws 151a, 1511); 152a, 152b; 53a, 153b. These contactreceiving jaws are mounted to the main portion 155 of plug-in base 150which is also provided with a plurality of locating apertures 151e,1520, and 153cin alignment with the respective pairs of contactreceiving jaws. Plug-in base 159 is also provided with an end portion156 which extends at right angles to main portion 155 and is stepped toprovide seats for terminals 157, 1 53.

Depressions 151a, 1520 and 1535c are adapted to receive a projection 159extending downwardly from the bottom of base 12 for positioning unit 10.With projection 159 of unit 16 disposed within depression 151a contactjaws 151a engage contact 40 and contact jaws 15112 engage contact 35.Similar units iii are mounted in the plug-in base 150 at locationsdefined by depressions 1520 and 1530.

Disposed within plug-in base 150 are conductors for establishing aseries circuit from terminal 157 to terminal 158 when three closedoverload relay units It) are mounted to base 150. Thus, conductor 165extends from terminal 157 to jaws 153b, conduct-or 166 extend from jaws153a to jaws 152b, conductor 167 extends from jaws 152a to jaws 151b,and conductor 168 extends from jaws 151a to terminal 158. As seen inFIGURE 7d jaws are formed on both ends of conductor 166 and formedintegrally therewith. For a situation where only the outer locationsdefined by depressions 1510 and 153c are to be utilized a strap isplaced between jaws 153a and jaws 1511).

With plug-in base 150 properly mounted at one end of contactor 2%, whenan overload relay unit is mounted to base 150 this unit it isautomatically positioned with the upturned portion Me of its mainterminal 16 abutting a main contact terminal 201 of contactor 200.

The embodiment of the invention in which an exclusive privilege orproperty is claimed are defined as follows:

1. An overload protective device comprising an electric heater, abimetal extending along a portion of said heater and closely spaced withrespect thereto, one end of said bimetal being movable with respect tosaid heater as a result of heat generated by electric current in saidheater, support means to which the other of said bimetal is mounted, aspring means in engagement with said support means and urging saidbimetal toward operative position relative to said heater, said supportmeans comprising a main support and an auxiliary support, said other endbeing fixedly secured to said main support, adjusting means for movingsaid main support relative to said auxiliary support by causing bendingof the latter.

2. An overload protective device comprising an electric heater, abimetal extending along a portion of said heater and closely spaced withrespect thereto, one end of said bimetal being movable with respect tosaid heater as a result of heat generated by electric current in saidheater, support means to which the other end of said bimetal is mounted,said support means comprising a main support and an auxiliary support,said other end being fixedly secured to said main support, firstadjusting means for moving said main support relative to said auxiliarysupport by causing bending of the latter, and second adjusting means,independent of said first adjusting means, for bodily moving saidbimetal and said supports as a unit relative to said heater.

3. The device of claim 2 in which there is a hollow base within whichthe heater, the bimetal, and the support means are disposed, a pivot forsaid unit as it is moved by said additional adjusting means, said pivotprovided by an internal formation of said base.

4. The device of claim 3 in which the first adjusting means ispositioned in the region of the one end of the bimetal and the secondadjusting means is positioned at a point between said adjusting meansand the other end of the bimetal with a portion of said additionaladjusting means positioned external of said base and said adjustingmeans positioned totally within said space.

5. An overload protective device comprising an electric heater, abimetal extending along a portion of said heater and closely spaced withrespect thereto, one end of said bimetal being movable with respect tosaid heater as a result of heat generated by electric current in saidheater, support means to which the other end of said himetal is mounted,a hollow base within which the heater, the bimetal, and the supportmeans are disposed, a pivot for said support means, said pivot providedby an internal formation of said base, and biasing means urging saidsupport means into abutment with said pivot.

6. The device of claim 5 in which there'is adjusting means for bodilymoving said bimetal and said support means as a unit about said pivotwith respect to said heater.

7. An overload protective device comprising an electric heater, abimetal extending along a portion of said heater and closely spaced withrespect thereto, one end of said bimetal being movable with respect tosaid heater as a result of heat generated by electric current in saidheater, support means to which the other end of said himetal is mounted,a pair of cooperating contacts, a contact arm carrying one of saidcontacts at one end thereof and being pivoted at its other end, a singletension spring connected at one of its ends to said contact arm, asupport for the other end of said spring, said support remaining fixedduring operation of said cooperating contacts, said spring and saidcontact arm arranged to form an overcenter toggle, a single memberconnecting said one end of said bimetal to said spring from operation ofsaid contact arm to open said contacts after predetermined deflection ofsaid bimetal upon heating thereof.

8. The device of claim 7 in which the single member provides a lostmotion connection between said spring and said bimetal as said bimetaldeflects upon cooling.

9. The device of claim 7 in which the spring is an elongated coiledmember and the single member engages the coiled member at a pointintermediate the ends thereof.

10. An overload protective device comprising an electric heater, abimetal extending along a portion of said heater and closely spaced withrespect thereto, one end of said bimetal being movable with respect tosaid heater as a result of heat generated by electric current in saidheater, support means to which the other end of said bimetal is mounted,a pair of cooperating contacts, a contact arm carrying one of saidcontacts at one end thereof and being pivoted at its other end, a singletension spring connected at one of its ends to said contact arm, saidspring and said contact arm arranged to form an over-center toggle, asingle member connecting said one end of said bimetal to said spring foroperation of said contact arm to open said contacts after predetermineddeflection of said bimetal upon heating thereof, an adjustable member towhich the other end of the spring is directly secured for establishingthe position of the spring Where said toggle will be over-center.

11. An overload protective device comprising an electric heater, abimetal extending along a portion of said heater and closely spaced withrespect thereto, one end of said bimetal being movable with respect tosaid heater as a result of heat generated by electric current in saidheater, support means to which the other end of said bimetal is mounted,a pair of cooperating contacts, a contact arm carrying one of saidcontacts at one end thereof and being pivoted at its other end, a singletension spring connected at one of its ends to said contact arm, saidspring and said contact arm arranged to form an over-center toggle, asingle member connecting said one end of said bimetal to said spring foroperation of said contact arm to open said contacts after predetermineddeflection of said bimetal upon heating thereof, a terminal strap havingdepression means defining pivot means for said other end of said contactarm, said spring biasing said other end into said depression means.

12. An overload protective device comprising an electric heater, abimetal extending along a portion of said heater and closely spaced withrespect thereto, one end of said bimetal being movable with respect tosaid heater as a result of heat generated by electric current in saidheater, support means to which the other end of said bimetal is mounted,a pair of cooperating contacts, a contact arm carrying one of saidcontacts at one end thereof and being pivoted at its other end, a singletension spring connected at one of its ends to said contact arm, saidspring and said contact arm arranged to form an over-center toggle, asingle member connecting said one end of said bimetal to said spring foroperation of said contact arm to open said 2,158,711 5/1939 Weber s200122 contacts after predetermined deflection of said bimetal 2,513,7487/1950 Schaefer 200-122 upon heating thereof, said contact arm includingan extcn- 2,740,013 3/1956 Waters 200-113 sion projecting beyond saidother end away from said one 2 314 3 11 1957 Wild r 200 122 end, a pairof auxiliary contacts one of which is mounted 5 2,831,943 4/1953 Ramseyet a1 1 to said extension whereby as said cooperating contacts are2,851,556 9/1958 vanvalkenburg 2O0 122 moved toward open and closedpositions said auxiliary 2 897 319 7/1959 Wolfi 200 122 contacts aremoved toward closed and open positions, 2:942:O81 6/1960 Ramsey et a1200 113 respectwely- 3,005,075 10/1961 Ellenberger 200 1 16 Referen sited by the Examiner 3,015,007 12/1961 Howard 200-414 UNITED STATESPATENTS BERNARD A. GILHEANY, Primary Examiner. 2,144,120 1/1934 Parks200122

1. AN OVERLOAD PROTECTIVE DEVICE COMPRISING AN ELECTRIC HEATER, ABIMETAL EXTENDING ALONG A PORTION OF SAID HEATER AND CLOSELY SPACED WITHRESPECT THERETO, ONE END OF SAID BIMETAL BEING MOVABLE WITH RESPECT TOSAID HEATER AS A RESULT OF HEAT GENERATED BY ELECTRIC CURRENT IN SAIDHEATER, SUPPORT MEANS TO WHICH THE OTHER OF SID BIMETAL IS MOUNTED, ASPRING MENS IN ENGAGEMENT WITH SAID SUPPORT MEANS AND URGING SID BIMETALTOWARD OPERATIVE POSITION RELATIVE TO SAID HEATER, SAID SUPPORT MEANSCOMPRIS ING A MAIN SUPPORT AND AN AUXILIARY SUPPORT, SAID OTHER ENDBEING FIXEDLY SECURED TO SAID MAIN SUPPORT, ADJUSTING MEANS